Internet Service Providers (ISPs) assign IP addresses to their users. This assignment is typically dynamic, for example, using dynamic host configuration protocol (DHCP). Computers that are connected to IP networks generally must be configured with an IP address before they can communicate with other computers on the network. A database may be provided for keeping track of computers that are connected to the network. Such a database can be used to prevent two computers from accidentally being configured with the same IP address. A network administrator for the ISP may reserve a range of IP addresses to be assigned to one or more client computers, and each client computer accessing the network through the ISP may be configured to request an IP address from the server during initialization of the client computer's connection to the network. The request-and-grant process may use a lease concept with a controllable time period, allowing the server to reclaim and then reallocate IP addresses that are not renewed at the end of the lease period. The server may also permanently assign an IP address to a requesting client from the reserved range defined by the administrator. In some cases, the server may keep a table of past IP address assignments, so that it can preferentially assign to a client the same IP address that the client previously had.